We have devised and are continuing to improve two different recombinant antigen delivery systems to analyze the immunological host responses to antigens specified by cloned genes. The first employs recombinant avirulent delta cya delta crp Salmonella strains, exhibiting stable high- level expression of cloned gene products in vivo due to use of a balanced-lethal host-vector system. The recombinant avirulent Salmonella strains target antigens to lymphoid tissues to induce secretory, humoral and cellular immune responses. The second employs oral immunization with plant meal prepared from transgenic plants expressing antigens specified by cloned genes to induce oral tolerance to overcome autoimmunity and local and possibly generalized secretory immune responses. The expressed antigens will include colonization and virulence antigens of pathogens, other bacterial antigens and allergens. Our objectives will be to (1) further improve and develop Salmonella antigen delivery systems to improve stability, immunogenicity, host specificity and containment, (2) use recombinant avirulent Salmonella expressing Streptococcus mutans colonization antigens to define the different and/or overlapping epitopes responsible for secretory, humoral and cellular immune responses, (3) use recombinant avirulent Salmonella expressing various antigens with and without fusion to an oral adjuvant to determine the influence of antigen amount, form and location in Salmonella on the type, level and duration of immune responses, (4) further improve and develop means for generating transgenic plants stably expressing high levels of foreign antigens specified by cloned genes, and (5) use transgenic plant materials containing foreign antigens for oral immunization of laboratory animals to investigate induction of local and generalized mucosal immune responses and the potential and means to induce tolerance. We will employ modern technologies in the fields of microbiology, immunology, genetics, molecular biology, microscopy, plant biotechnology and animal science in our research.